This invention relates to encoders for meter dials for use in remote meter reading systems, and more particularly to meter dial registers of the multi-dial type having a binary encoder including a single track code pattern and pattern sensing assembly with a single row of sensing positions for converting the angular positions of the register pointer shafts to a binary code signal in a suitable form for telemetering the meter reading to a remote location.
It is well known to provide utility meters having gear-driven registers of the dial type with encoding arrangements for converting the dial shaft positions to a binary code. Meter registers equipped with encoders provide a convenient way to convert the dial readings of existing utility meters to signals linked to a remote meter reading system with the registers still being usable in the conventional mode for providing visual readings. The binary encoded or digitized meter reading signals can be compared to the register dial readings to check if there is any error in the encoder signals. Also, in the event of a malfunction of the encoder or the associated remote meter reading telemetry system, there remains the normally provided dial readings to determine the billing of a utility customer.
Examples of prior art meter dial encoders of a similar type to which the present invention pertains are disclosed in U.S. Pat. Nos. 2,067,098, 3,310,801, 3,806,875, 3,846,788, 3,846,789 and 3,683,368. The aforementioned patents disclose encoders for electric utility meter registers for use in conventional watthour meters connectable to a remote meter reading system. Generally, registers included in the aforementioned patent references have four or five decade dials, each with a shaft-driven pointer. A code pattern and a pattern sensing device is associated with each of the pointer shafts. Either the pattern or the sensing device is movable in response to the meter indicating movement of the shaft. Typically, optical or contact wiper type of arrangements are provided in the encoder code pattern and sensor systems. One difficulty in the wiper arrangements is that the coded conductive segments are subjected to continuous wear by a brush wiper which alternately develops conductive and non-conductive sensor signals. The optical arrangements generally include reflective or apertured coded segments and associated radiation or light sources directed at the coded segments. A complementary radiation or light sensing arrangement is optically aligned with the segments. U.S. Pat. No. 3,806,875 discloses bundles of optical fibres for transmitting light to and from coded tracks of drums driven by the shaft of a measuring device. Difficulties presented in the optical arrangements include the precision manufacture of accurate code segments in or on usually very small discs. Also, these code discs must be precisely mounted on the register pointer shafts in precise orientations which will not slip relative to the shafts. The optical light sources and sensing arrangements must be precisely mounted within the registers adjacent the code discs. Electrical and electronic circuitry must be further mounted therein to produce the desired scanning and output arrangements of the sensors to develop binary code signals from the meter.
In addition to the aforementioned considerations, the encoders must be extremely rugged and reliable and operable at widely varying temperature and ambient conditions consistent with the normally designed extended use features of utility meters. The size and complexity of encoders are limited by the size and complexity of the registers. Gear train mechanisms are included in the registers in relatively small and compact spaces to produce the ten to one ratios between the register decade dials. It is necessary to provide the code patterns so that there is capability of interdial interpretation for determining the pointer position of one dial relative to the adjacent next less significant dial reading just as such interpretations are required upon visual reading of the dials. Further, it is desirable that there be a provision for detecting when an error occurs in the coded meter reading signals. It should be understood that the complexity of the code patterns increase as the resolution or amounts of shaft angular movement increases in accuracy to produce a different and unambiguous signal. The aforementioned considerations in meter register encoders are generally understood by those skilled in the art and are noted in the above-identified prior patents.